1. Field of the Invention
The present invention relates to an optical-fiber cable having a cylinder body disposed at the center, with optical-fibers being accommodated in the cylinder body, and relates, more particularly, to an optical-fiber cable which can be manufactured easily at low cost by forming a belt-shaped material into a cylinder shape to form a cylinder body.
2. Description of Related Art
There have been known 1) a slot type cable, 2) a loose tube type cable and 3) a center tube type cable, for example, as structures of an optical-fiber cable for assembling several tens to several hundreds of optical-fibers together.
According to the slot type cable, optical-fiber ribbons are accommodated within grooves that is formed on the outer peripheral surface of a rod, and a pressed-wound layer and a sheath are formed sequentially on the periphery of the slotted rod. A tension member is disposed at the center of the slotted rod, with a rip cord disposed between the pressed-wound layer and the sheath.
According to the loose tube type cable, loose tubes accommodating optical fibers are stranded around central tension members, and a pressed-wound layer and a sheath are formed sequentially on this assembly. Jelly is filled within the loose tubes, and rip cords are distributed between the pressed-wound layer and the sheath.
According to the center tube type cable, there is disposed, at the center, a center tube accommodating optical-fiber ribbons therein, and a sheath is formed on the periphery. Tension members are embedded within the sheath, and jelly is filled within the center tube. Further, rip cords are disposed between the center tube and the sheath.
These optical-fiber cables have had the following problems.
The slot type cable has a suitable structure for obtaining a multiple-core optical-fiber cable as the optical-fibers are accommodated in the spiral grooves formed on the outer periphery of the rod. However, the slot type cable has a problem that its structure becomes costly in the case of a small-core optical-fiber cable due to high cost of the slotted rod.
The loose tube type cable has a suitable structure for obtaining a small-core optical-fiber cable by using single-core optical-fibers. However, the loose type cable has a problem of having a larger number of manufacturing processes because this structure requires a process of forming loose tubes and a process of assembling a plurality of loose tubes around a central tension member. Further, in the case of structuring a multiple-core optical-fiber cable by using optical-fiber ribbons, this has a problem that an external diameter becomes larger. Furthermore, as the loose tubes are manufactured by a method of forming a tube by extruding a resin while inserting optical-fibers at the same time, it has been unavoidable to charge jelly into the whole inside of the loose tubes in order to prevent a molten resin from adhering to the optical-fibers at the time of forming by extrusion. Accordingly, this has an inconvenience of incurring the cost of charging the jelly.
The center tube type cable can be manufactured in a relatively small number of processes because of its simple structure. However, the center tube is formed by extrusion while inserting optical-fibers and optical-fiber ribbons at the same time, as in the case of the loose tube type cable. Therefore, it has been unavoidable to charge jelly into the tubes in order to prevent a move of the optical-fiber ribbons in a longitudinal direction within the center tube. This has a problem of high manufacturing cost.
Moreover, both the loose tube type cable and the center tube type cable have had a problem that the tube has to be disconnected at the time of carrying out a connection such as a branch connection or the like.